山东诸城早白垩世中期超大规模恐龙足迹群及其古地理与古生态

摘要

Theropod,sauropod and possible ornithopod dinosaur tracks were mainly developed in the middle Early Cretaceous Yangjiazhuang Formation,Laiyang Group,in Zhucheng area,Shandong Province.Most of them are theropod tracks,and belong to three types:Large sized theropod,Paragrallator and Corpulentapus lilasia.Among the 63 trackways identified,50 well-preserved trackways were measured systematically.Based on the foot size index-stride length diagram and GAE (Grallator-Anchisauripus-Eubrontes) plexus,we obtained the differential criteria for the theropod tracks.Large scale sections in the track site showed that shallow lake silty mudstone and siltstone gradually changed to shore-lacustrine sandstone.Track beds and the upper and lower beds developed abundant wavemarks and mud cracks.According to the wave crest,we reconstructed the palaeoshoreline which was EW in direction.The direction of the wave flow showed N-NW periodical change,which may be correlated with shift in the direction of the seasonal wind.The mud crack and the feature of dinosaur track distribution indicated that the center of the lake should be S/WS in direction,while lakeshore should be N/NE in direction.The differences in distribution area between Paragrallator and Corpulentapus lilasia revealed that the Corpulentapus lilasia track makers were living much closer to the lake shore.The phenomenon of superposition is common among dinosaur tracks,which indicated that the tracks were not left at the same time but in several times.Lots of parallel small-medium sized trackways represent gregarious habitats.Speed study showed that most of theropods were running fast,in contrast,sauropods and suspected ornithopods were walking slowly.The proportion between theropod tracks and sauropod and suspected ornithopod tracks indicated that in the middle Early Cretaceous,small-medium sized theropods were dominant in Jiaolai Basin,while sauropods and suspected ornithopods were less; in contrast,sauropods,ornithopods and avians gradually flourished in Jiaolai Basin and Yishu Fault Belt,which was consistent with the dinosaur tracks in northern North China.A comparison of the Cretaceous dinosaur tracks and bones has been made among northern China,Korea and Japan,proposing that a large-scale terrestrial biota represented by dinosaur existed in northern China and eastern Asia during late Mesozoic.%山东诸城黄龙沟恐龙足迹产于下白垩统中部莱阳群杨家庄组,其中以兽脚类为主,同时有蜥脚类和疑似鸟脚类足迹;兽脚类足迹又可进一步区分为大型兽脚类、似跷脚龙类(Paragrallator)和东方强壮百合龙类(Corpulentapus lilasia).足迹共组成至少63条行迹,作者系统实测了其中50条,并据足迹大小指数一复步长和GAE(跷脚龙一安琪龙一实雷龙)图解给出了识别3类兽脚类足迹的经验性数值.足迹点沉积特征显示,浅湖相粉砂质泥岩和粉砂岩逐渐过渡为滨湖相砂岩.足迹层及其邻近层位波痕、泥裂发育,根据波脊线恢复的古岸线方向为东西向,波浪运动方向呈现出北至北西周期性变化,表明可能存在季节性风向变化.泥裂以及恐龙分布特征显示足迹点以S/WS为湖心方向,以N/EN为湖岸方向.似跷脚龙类和东方强壮百合龙类足迹分布区域的差异性表明东方强壮百合龙类生活区域更靠近湖岸.恐龙足迹中存在的明显叠盖现象表明足迹不是同时,而是多次活动遗迹.小型兽脚类行迹中较多近于平行的行迹体现了集群性生活习性.行进行为研究又显示兽脚类的绝大多数为快速奔跑状态,但蜥脚类等为慢行状态.兽脚类与蜥脚类、疑似鸟脚类足迹数量之比远大于正常捕食者和被捕食者之比也表明,早白垩世中期的胶莱盆地生存着以兽脚类为主、蜥脚类和鸟脚类为辅的恐龙动物群.早白垩世晚期,胶莱盆地以及沂沭断裂带内蜥脚类、鸟脚类恐龙以及鸟类逐渐繁盛,这与华北北部恐龙足迹所恢复的造迹恐龙动物群特征较为一致.中国北方、韩国、日本白垩纪恐龙足迹以及骨骼化石发育情况暗示,晚中生代中国北方以及东亚地区发育一个以恐龙等脊椎动物为主的大型陆地动物群.